1. Field of the Invention
The present invention relates to a method, an apparatus and a computer program product for the classification of measured data from a multi-core optical fiber in which the multi-core optical fiber comprising a plurality of core optical fibers each of which has a plurality of connection points is subject to an optical pulse test, and the measured waveform data obtained from the test is then analyzed to determine the amount of loss at the connection points and the amount of reflection at the reflection points for each core optical fiber in the optical fiber path, and these amounts are classified for each core optical fiber and a classification table then produced. More specifically it relates to a technique for generating a file called a master file which is used by a measured data classification apparatus for classification processing. The present invention is based on Japanese Patent Application No. Hei-10-137227, the content of which is incorporated as a portion of this application.
2. Description of the Related Art
The provision of optical fiber networks is essential in realizing a multimedia networked society. Consequently, provision of this type of optical fiber network has centered on main trunk systems. In recent years however, there has been a rapid expansion of optical fiber networks to include subscriber systems. Optical fiber measuring devices such as OTDR (Optical Time Domain Reflectometer) apparatus are used to sustain the expansion of these optical fiber networks. OTDR apparatus are also known as optical fiber analyzers and optical pulse testing devices. By using an OTDR apparatus, the loss distribution in a longitudinal direction along an optical fiber can be viewed directly from one end of the optical fiber, and so these apparatus have been widely used in optical fiber applications.
Furthermore, the provision of optical fiber networks has required large amounts of cable to be laid, as well as the classifying of various data obtained from measurements of the optical fiber paths which is used for managing maintenance of the networks. To explain in more detail, there are typically between 1000 and 2000 core optical fibers laid between two stations. In order to conduct tests or carry out maintenance on an optical fiber path such as this, which comprises a plurality of core optical fibers each of which has a plurality of connection points, an OTDR apparatus conducts an optical pulse test on each of the core optical fibers, and based on the measurement results obtained from the tests, creates a classification table for every core optical fiber, of information such as the connection loss and amount of reflection (hereafter referred to as the characteristic data of the optical fiber) at the fusion points and connector connection points (hereafter referred to as events, or event points) of the optical fiber. Based on this classification table, judgements are made as to whether the loss value at a fusion point exceeds the standard value, or whether there is a break in the line.
Heretofore, the classification operation has been conducted in the manner described below. First, the operator randomly selects, for example, three core optical fibers from the plurality of core optical fibers, and then using an OTDR apparatus conducts an optical pulse test on each of the core optical fibers chosen, with the waveform data thus obtained being used to generate a loss distribution measured waveform, which can then be displayed on a screen, for example. The operator then inspects the measured waveform displayed for event points, and marks the location of any event points present in the measured waveform.
FIG. 7 shows an enlargement of one portion of a loss distribution measured waveform measured by an OTDR apparatus. In the figure, the horizontal axis represents the distance, referenced against the OTDR apparatus, from the OTDR apparatus to a position in the optical fiber path, and the vertical axis represents the optical level of return light such as backward scattered light and Fresnel reflected light occurring in the optical fiber path.
As shown in the figure, each of the core optical fibers C1.about.C3 displays an event point indicated by a level difference which represents a connection loss resulting from fusion of the optical fiber. In this case, the operator would set markers M1 and M2 in the measured data classification apparatus to include all of these event points occurring within the core optical fibers C1.about.C3. Furthermore, in the figure, because the event points represent fusion points, the operator must also make settings in the measured data classification apparatus which convey this information. Hereafter the information which conveys whether each event point is a fusion point or a reflection point is termed the "connection classification". For every event point not shown in FIG. 7 then, the operator must set a marker on either side of the event point as well as a connection classification. These markers and connection classifications are not set for each individual core optical fiber, but rather are set as data common to all core optical fibers.
The measured data classification apparatus stores the data set by the operator in a file inside the measured data classification apparatus known as a "master file". The data collected when an OTDR apparatus is used to perform an optical pulse test on an optical fiber path, includes not only the marker locations (explained below in further detail) and connection classifications set using the OTDR apparatus for each event point, but also various data relating to factors other than the event points such as the distance range corresponding to the length of the optical fiber path to be measured, and the pulse width of the optical pulse to be input into the optical fiber path in accordance with the distance range. The aforementioned master file is of the same format as this data collected by the OTDR apparatus.
Once the operator has set markers for all the event points, the measured data classification apparatus investigates, based on the master file, the measured waveform data for each core optical fiber between the markers M1 and M2 set for each event point and determines whether or not an event occurs, and then computes for all of the approximately 1000.about.2000 core optical fibers the amount of loss at the fusion points and the amount of reflection at the reflection points. The measured data classification apparatus then generates a classification table, based on the computed results obtained, of the connection loss value and the amount of reflection for each core optical fiber at each event point, and displays this classification table on screen.
As described above, in conventional measured data classification apparatus, markers and connection classifications for each event point based on the measured waveforms are set only for the several core optical fibers randomly selected by the operator from a great number of core optical fibers. The markers and connection classifications set in this manner are then considered to be common to all of the core optical fibers, and the connection loss value and the amount of reflection are then investigated for each event point. That is, because the setting of the marker locations is performed manually by the operator, it is impractical for the operator to set markers for all of the 1000.about.2000 core optical fibers. Consequently, the measured data classification apparatus sets the marker locations based solely on the measured waveforms obtained from the limited number of core optical fibers selected by the operator.
Even with the use of this type of marker location setting procedure, provided there is very little variation between core optical fibers in terms of the distance at which an event point occurs, no particular problems arise. However, in a multi-core optical fiber it is extremely rare for the locations (distances) at which events occur to be identical across different core optical fibers, and a certain amount of variation is usual. Consequently, as shown in FIG. 8, if the operator has used core optical fibers C1.about.C3 to set the markers M1 and M2 to indicate the range in which an event occurs, and a core optical fiber Cn then exists in which the same event occurs outside of this marked range, then the connection loss value and the amount of reflection relating to this event point cannot be classified for this particular core optical fiber Cn.
In order to prevent this type of problem, it should be possible to take into consideration the variation in event point location across the core optical fibers and include, for a single event point, the core optical fiber with the shortest distance and that with the longest distance, by moving the set location of the marker M1 further left, for example. However, because an optical fiber has as many as 1000.about.2000 core optical fibers, in reality the burden on the operator becomes enormous. In fact, it is virtually impossible for the operator to conduct this type of adjustment of the marker locations for every core optical fiber.
In addition to the above problems, in those cases where due to factors such as the precision of the fusion the connection loss is not particularly large and generates only a small level difference, the operator is sometimes unable to recognize an event point by just viewing the measured waveform. That is, as shown in FIG. 9, despite the fact that a fusion event point exists between the markers M1 and M2 in all of the core optical fibers C1.about.C3 selected by the operator, because the connection loss is almost negligible it becomes very difficult to determine whether or not an event point exists based only on the measured waveform displayed on the screen. If as a result, no markers are set for an event point, then even if there is a significant connection loss in core optical fibers other than the selected core optical fibers C1.about.C3, the connection loss will not be classified for this event for any of the core optical fibers. Of course, it can be said that rather than limiting the number of core optical fibers selected to three fibers, the operator could set marker locations for a larger number of core optical fibers. However, the maximum number of core optical fibers which need to be investigated to alleviate the problems is of course ill-defined. Furthermore, increasing the number of core optical fibers to be examined to several dozen increases the work burden on the operator enormously, and cannot be considered a practical solution.